Anhydrous sodium methylate

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This page gives a guide to making Biodiesel from anhydrous sodium methylate (ASM), a liquid catalyst which can be used in place of the more conventional sodium hydroxide or potassium hydroxide catalysts.

Anhydrous sodium methylate (ASM) is a white powder in pure form but for practical use as a catalyst in diy biodiesel it is dissolved in pure methanol at 25% to 30% concentration. In this form it is a colourless, viscous fluid with a slightly sweet alcohol smell - very similar to methanol which, after all, makes up a large proportion of the fluid volume. ASM is both highly flammable, corrosive and toxic through inhalation, skin contact and ingestion. It evaporates readily to leave a white powdery residue and at low temperatures it tends to precipitate out as a colouless crystal.


Compared to sodium hydroxide and potassium hydroxide which are readily available from a number of chemical suppliers around the UK, ASM is somewhat harder to source. One well known biodiesel chemical supplier does sell it in various pack sizes from 25litre HDE cans to 1000litre IBCs and new sources are starting to appear. Current (Sept 2012) prices are in the £1.50 to £2.20 per litre range

As of 2019 Anydrous Sodium Methylate has become increasingly difficult to source due to regulations relating to storage.


Shelf life of ASM is quoted as 12 months from delivery if kept dry and in original packaging. Storage temperature should not exceed 30°C, and at temperatures below 10°C the active ingredient may start to precipitate. Warming, combined with agitation will help re-dissolve the active ingredient.

Crystallisation temperatures of ASM solutions:

  • 25% ... -2°C
  • 28% ... 0°C
  • 30% ... 5°C

The pros and cons of using anhydrous sodium methylate


  • Mixing it with methanol is as easy as making orange squash
  • Being a liquid, there is no corrosive dust to worry about
  • Being around 70% methanol, using methylate requires less methanol in the batch


  • Methylate is considerably more expensive than solid catalysts although this can be offset against methanol savings
  • Availability is still an issue although this is improving

Julesandtash 21:11, 15 September 2012 (BST)